CI: build with Ruby 3.4

Author: phw

.github/workflows/test.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.0', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', 'jruby']
+        ruby-version: ['2.0', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', '3.4', 'jruby']
 
     steps:
     - uses: actions/checkout@v3